Computing devices, such as tablets and notebook computers, smartphones and other mobile devices, portable entertainment devices (e.g., handheld video games, multimedia players, etc.), and set-top-boxes (e.g., digital cable boxes, digital video disc (DVD) players, etc.) may include user interface devices that facilitate interaction between a user and the computing device. One type of user interface device that has become common is a touch-input device (e.g., such as a touch-sensor device) that operates by way of capacitance sensing. A touch-input device may be in the form of a touchscreen, touch-sensor pad, touch-sensor slider, or touch-sensor buttons, and may include a sensor comprising and/or coupled to an array of capacitive sensor elements. Capacitive sensing typically involves scan operations that periodically measure changes in capacitance associated with the sensor elements to determine a presence, position, and/or movement of an object (e.g., a stylus, a user's finger, etc.) relative to a touch-input device.
For proper operation, a touch-input device needs to be able to correctly detect and reject contacts caused by non-conductive objects and/or contacts caused through a leather or plastic cover by any object (conductive and non-conductive alike). However, conventional detection and rejection mechanisms typically involve computationally-intensive processing that often limits the functionality of the touch-input device and/or leads to poor user experience.